Don't expose raw usage stats to clients; return "low-res" values.

Test: run-all-tests.sh
Test: cts-tradefed run cts-dev --skip-device-info --skip-preconditions --skip-system-status-check \
  com.android.compatibility.common.tradefed.targetprep.NetworkConnectivityChecker -a armeabi-v7a \
  -m CtsProviderTestCases

Bug 31753890

Change-Id: Ie71af1ab31d74fed69342f91304d3718e3ccd133